1. Field of the Invention
The present invention relates to computer networking and in particular to modifying data transferred from a source to a destination.
2. Background Information
A computer network is a geographically distributed collection of interconnected network links and segments for transporting data between nodes, such as computers. Many types of network segments are available, with the types ranging from local area networks (LANs) to wide area networks (WANs). End nodes, such as personal computers or workstations, typically communicate over the network by exchanging discrete frames or packets of data according to predefined protocols. In this context, a protocol consists of a set of rules defining how the nodes interact with each other.
Computer networks may be further interconnected by an intermediate node, such as a switch or router, having a plurality of ports, which may be coupled to the networks. For example, a switch may be utilized to provide a “switching” function for transferring information between a plurality of LANs at high speed. The switching function includes receiving a data packet at a source port that originated from a source node and transferring that packet to at least one destination port for forwarding to a destination node.
A router may be used to interconnect LANs executing different LAN standards and/or to provide higher-level functionality than a switch. If the LAN standards associated with the source and destination nodes are dissimilar (e.g., Ethernet and token ring), the router may also alter the format of the packet so that it may be received by the destination node. Routers typically operate at the network layer of a communications protocol stack used by the network, such as the internetwork layer of the Transmission Control Protocol/Internet Protocol (TCP/IP) communications architecture.
Routers also perform various functions associated with modifying data transferred from a source to a destination, such as processing packets received by the router. These functions may include inserting, deleting, or replacing information in a packet. For example, some routers support the Multi-Protocol Label Switching (MPLS) protocol. The MPLS protocol provides a method of assigning labels that instructs routers where to send a packet and the priority that packet should receive. In accordance with MPLS, packets are transmitted on a label-switched path (LSP). An LSP is a simplex path that typically comprises a sequence of labels that represent every node along the path from a source label-edge router (LER) to a destination LER. An LER is a device (e.g., router) that operates at the edge of the access network and MPLS network, and is typically involved in the assignment and removal of LSPs, as traffic enters or exits an MPLS network. In a typical arrangement, an LSP is generated by concatenating the labels to form the path. The LSP is then inserted into the packet's header at the source LER. When the packet reaches the destination LER, the labels are deleted (removed) from the packet's header and the packet is further processed, e.g., the packet may be forwarded.
An LER often employs a processor (CPU) to insert and delete the LSPs contained in the packets carried over an MPLS network. Usually, the processor also performs other tasks for the LER, such as implementing various routing protocols and generally managing the LER. However, employing the processor to insert and delete LSPs in packets may not be an efficient use of the processor's resources. Inserting and deleting LSPs often consumes time and memory resources, and may waste valuable processor resources that could be better employed performing other tasks, such as executing routing protocols.
For example, generating and inserting an LSP into a packet often involves (i) generating the LSP by moving various pieces of data from various memory locations into a single memory area and (ii) inserting the LSP into the packet's header, which may further involve breaking the packet header into leading and lagging portions prior to inserting the LSP between the portions. Clearly this process involves a great deal of computing resources and memory bandwidth. Depending upon the amount of traffic processed, an inordinate amount of processor resources may be dedicated to modifying the data traffic, e.g., processing LSPs, which may impact the processor's ability to perform other tasks, such as processing other packets, managing routing tables, and responding to other routers in the network. This in turn may result in decreased packet processing performance (i.e., packet throughput) of the router. Moreover, in some cases these tasks may be time-critical, requiring the processor to complete the task within a certain time window. An example of such a task is the sending of a “keep-alive” packet within a certain time frame in order for the router to be acknowledged by the network. If the processor dedicates a substantial portion of its resources modifying data transferred from a source to a destination, it may not have sufficient resources left to perform these time-critical tasks.